Conventionally, to measure inner diameter dimension of a fine cylindrical work such as a ferrule, the operator inserts pin gauges of predetermined sizes in an inner periphery of the work. For automatic measurement, the work is placed on a V table or the like, the work is rotated with a probe of a contact type displacement gauge kept in contact with its inner periphery, and the inner diameter dimension of the work is determined from the amount of displacement of the probe. Alternatively, as disclosed in Japanese Patent Application Publication No. 8-29642, Japanese Patent Application Publication No. 10-227619, and Japanese Patent Application Publication No. 6-174433, for example, the work is placed on a V table or the like, images of its end face are picked up with a CCD camera while it is rotated, and the resulting image data is subjected to image processing to determine the inner diameter dimension of the work.
However, the method which uses pin gauges has the drawback of requiring the operator to expend a great deal of effort measuring each work manually. Also, it has the drawback of lacking accuracy because of manual work. Furthermore, it has the drawback that the pin gages, which are inserted, get worn as measurements are taken repeatedly, resulting in inaccurate measurements.
On the other hand, the method which uses automatic measurements has the drawback of taking time for measurements because the work must be rotated for each measurement. Also, it has the drawback of needing a mechanism for rotating the work, resulting in increased equipment size. Furthermore, it has the drawback that the V table or the like gets worn, resulting in inaccurate measurements because the V table or the like is rotated with a work mounted on it. Besides, it has the drawback that a contact type displacement gauge, which involves inserting the probe in the inner periphery of the work, cannot measure small-diameter works such as ferrules because there are limits to diameters that can be measured. On the other hand, the method which uses image processing has the drawback of being able to measure only end face diameters.
The present invention has been made in view of the above problems and has an object to provide an inner diameter measuring method and device which can measure inner diameter dimensions of works easily and accurately with a simple configuration.